`dcgain` — Evaluate steady-state gain of SISO transfer-function models.

dcgain(sys) evaluates a SISO transfer function at s = 0 for continuous-time models or z = 1 for discrete-time models.

Syntax

gain = dcgain(sys)

Inputs

Name	Type	Required	Default	Description
`sys`	`Any`	Yes	—	SISO tf model.

Returns

Name	Type	Description
`gain`	`Any`	Steady-state gain evaluated at s=0 for continuous-time or z=1 for discrete-time.

Errors

Identifier	When	Message
`RunMat:dcgain:InvalidArgument`	Input does not match supported invocation forms.	`dcgain: invalid argument`
`RunMat:dcgain:InvalidModel`	Input system is not a valid SISO tf object.	`dcgain: invalid model`
`RunMat:dcgain:UnsupportedModel`	Model form is not supported by the current implementation.	`dcgain: unsupported model`
`RunMat:dcgain:Internal`	Gain evaluation failed internally.	`dcgain: internal error`

How `dcgain` works

Supports SISO tf objects.
Returns a real scalar for real-valued gains and a complex scalar for complex-valued gains.
Continuous-time models are evaluated at zero frequency.
Discrete-time models are evaluated at z = 1.

GPU memory and residency

dcgain returns a host scalar.

Example

Continuous-time DC gain

H = tf(2, [1 3]);
dcgain(H)

Expected output:

ans = 0.6667

How RunMat validates `dcgain`

dcgain validates the input model and evaluates numerator and denominator polynomials at the steady-state point. Tests cover real continuous-time gains and VM integration.

Implementation: `crates/runmat-runtime/src/builtins/control/dcgain.rs`

See Correctness & Trust for the full methodology and coverage table.

Using `dcgain` with coding agents

Open a RunMat example with live inputs, then ask the agent to explain how dcgain changes the result.

Run a small dcgain example, explain the result, then change one input and compare the output.

FAQ

Does dcgain simulate a step response?⌄

No. It evaluates the transfer-function polynomials directly at the steady-state point.

db · feedback · impulse · isstable · nyquist · pole · ss · step · stepinfo · tf

Open-source implementation

Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how dcgain is executed, line by line, in Rust.

View the source for dcgain in Rust on GitHub
Learn how the RunMat runtime works
Found a bug? Open an issue with a minimal reproduction.

About RunMat

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dcgain — Evaluate steady-state gain of SISO transfer-function models.